The covering method: an improved negative staining method for ultrathin cryo-sections of tissue.

Ultrathin cryo-sections of biological tissues for electron microscopy provide numerous advantages in cytochemical and morphological studies. However, difficulties still remain in the application of negative staining to cryo-sections. This paper describes a method for negative staining of cryo-sections by covering the grid with a piece of either Collodion or Formvar film. By doing so, appropriate amount of staining solution is retained on the grid for positive effects. Also, the present method requires only a few seconds to stain the ultrathin cryo-sections while previously published methods took up to 10 min.